Electron tunneling time measured by photoluminescence excitation correlation spectroscopy

The tunneling time for electrons to escape from the lowest quasibound state in the quantum wells of GaAs/AlAs/GaAs/AlAs/GaAs double-barrier heterostructures with barriers between 16 and 62 Å has been measured at 80 K using photoluminescence excitation correlation spectroscopy. The decay time for samples with barrier thicknesses from 16 Å (≈12 ps) to 34 Å(≈800 ps) depends exponentially on barrier thickness, in good agreement with calculations of electron tunneling time derived from the energy width of the resonance. Electron and heavy hole carrier densities are observed to decay at the same rate, indicating a coupling between the two decay processes

Extremal Black Hole/CFT Correspondence in (Gauged) Supergravities

We extend the investigation of the recently proposed Kerr/CFT correspondence to large classes of rotating black hole solutions in gauged and ungauged supergravities. The correspondence, proposed originally for four-dimensional Kerr black holes, asserts that the quantum states in the near-horizon region of an extremal rotating black hole are holographically dual to a two-dimensional chiral theory whose Virasoro algebra arises as an asymptotic symmetry of the near-horizon geometry. In fact in dimension D there are [(D-1)/2] commuting Virasoro algebras. We consider a general canonical class of near-horizon geometries in arbitrary dimension D, and show that in any such metric, the [(D-1)/2] central charges each imply, via the Cardy formula, a microscopic entropy that agrees with the Bekenstein-Hawking entropy of the associated extremal black hole. In the remainder of the paper we show for most of the known rotating black hole solutions of gauged supergravity, and for the ungauged supergravity solutions with four charges in D=4 and three charges in D=5, that their extremal near-horizon geometries indeed lie within the canonical form. This establishes that in all these examples, the microscopic entropies of the dual CFTs agree with the Bekenstein-Hawking entropies of the extremal rotating black holes.Comment: 32 pages, references added and minor typos fixe

Single-charge rotating black holes in four-dimensional gauged supergravity

We consider four-dimensional U(1)^4 gauged supergravity, and obtain asymptotically AdS_4, non-extremal, charged, rotating black holes with one non-zero U(1) charge. The thermodynamic quantities are computed. We obtain a generalization that includes a NUT parameter. The general solution has a discrete symmetry involving inversion of the rotation parameter, and has a string frame metric that admits a rank-2 Killing-Stackel tensor.Comment: 9 page

Running-phase state in a Josephson washboard potential

We investigate the dynamics of the phase variable of an ideal underdamped Josephson junction in switching current experiments. These experiments have provided the first evidence for macroscopic quantum tunneling in large Josephson junctions and are currently used for state read-out of superconducting qubits. We calculate the shape of the resulting macroscopic wavepacket and find that the propagation of the wavepacket long enough after a switching event leads to an average voltage increasing linearly with time.Comment: 6 pages, 3 figure

Symmetries of supergravity black holes

We investigate Killing tensors for various black hole solutions of supergravity theories. Rotating black holes of an ungauged theory, toroidally compactified heterotic supergravity, with NUT parameters and two U(1) gauge fields are constructed. If both charges are set equal, then the solutions simplify, and then there are concise expressions for rank-2 conformal Killing-Stackel tensors. These are induced by rank-2 Killing-Stackel tensors of a conformally related metric that possesses a separability structure. We directly verify the separation of the Hamilton-Jacobi equation on this conformally related metric, and of the null Hamilton-Jacobi and massless Klein-Gordon equations on the "physical" metric. Similar results are found for more general solutions; we mainly focus on those with certain charge combinations equal in gauged supergravity, but also consider some other solutions.Comment: 36 pages; v2: minor changes; v3: slightly shorte

Muonium as a shallow center in GaN

A paramagnetic muonium (Mu) state with an extremely small hyperfine parameter was observed for the first time in single-crystalline GaN below 25 K. It has a highly anisotropic hyperfine structure with axial symmetry along the [0001] direction, suggesting that it is located either at a nitrogen-antibonding or a bond-centered site oriented parallel to the c-axis. Its small ionization energy (=< 14 meV) and small hyperfine parameter (--10^{-4} times the vacuum value) indicate that muonium in one of its possible sites produces a shallow state, raising the possibility that the analogous hydrogen center could be a source of n-type conductivity in as-grown GaN.Comment: 4 figures, to be published in Phys. Rev. Letter

Threshold effects in excited charmed baryon decays

Motivated by recent results on charmed baryons from CLEO and FOCUS, we reexamine the couplings of the orbitally excited charmed baryons. Due to its proximity to the [Sigma_c pi] threshold, the strong decays of the Lambda_c(2593) are sensitive to finite width effects. This distorts the shape of the invariant mass spectrum in Lambda_{c1}-> Lambda_c pi^+pi^- from a simple Breit-Wigner resonance, which has implications for the experimental extraction of the Lambda_c(2593) mass and couplings. We perform a fit to unpublished CLEO data which gives M(Lambda_c(2593)) - M(Lambda_c) = 305.6 +- 0.3 MeV and h2^2 = 0.24^{+0.23}_{-0.11}, with h2 the Lambda_{c1}-> Sigma_c pi strong coupling in the chiral Lagrangian. We also comment on the new orbitally excited states recently observed by CLEO.Comment: 9 pages, 3 figure

Understanding the Economic and Political Effects of Trump\u27s China Tariffs

Although President Trump has persistently claimed that China is paying billions of dollars in tariffs imposed on Chinese imports to the United States, empirical evidence indicates that U.S. consumers are bearing the cost of the tariffs: $51 billion in increased prices and a net loss of$7.2 billion to the U.S. economy. The unilateral power-based approach to trade used by the Trump Administration has also resulted in unexpected economic and political costs in key Midwestern states that helped propel Trump to the U.S. presidency in 2016. These costs have led to reverses for the Trump Administration in the mid-term elections of 2018 and could ensue in further electoral losses. As both political parties currently hold little affection for China, the United States could continue to use tariffs against China and other countries as trade policy no matter which party controls the U.S. presidency. For these reasons, a study of how to most effectively use a power-based approach to trade is both useful and timely. This study indicates that a power-based approach can be used most effectively against countries that lack either the economic power or the political will to engage the United States in a prolonged trade standoff. While most nations appear to fall into one or both of these categories, China is not one of them. China has the economic power to fight a trade war, and China believes it must stand up to the United States. When used against China, the power-based approach carries greater risks because its economic and political effects are difficult to predict and because this approach is inherently more uncertain than the cooperative approach of the World Trade Organization that the United States has rejected. Using a power-based approach against China could backfire because China has the economic power and political will to endure a prolonged battle and play a dangerous game of mutual pain and destruction with the United States

Renew : a renal redesign project in predialysis patient care

Background: An ageing population and geographical growth, along with an increase in the number of people that reside in specific location, are increasing the demand for renal replacement therapies. Hospital-based haemodialysis units are struggling to cope with the associated physical, staffing and cost demands. Home-based dialysis therapies are known to be more cost effective with superior social, physical health and survival outcomes. Methods: 'RENEW, a renal redesign project, examined the pre-dialysis health care experience of renal patients to find opportunities to improve patient care outcomes and increase the uptake of home-based dialysis therapies. This article details two crucial parts of the approach to change management: (i) diagnostics-An inclusive, client focused, multidisciplinary approach to identify issues relating to the pre-dialysis journey-And (ii) solution design-An inclusive problem-solving approach to identify and marry solutions to the issues identified during diagnostics. Results: Based on feedback from patients/caregivers and staff interviews, utilizing a clinical redesign methodology, a new model of care was developed, implemented and subsequently embedded into clinical practice. The results have been evident via improved care coordination, enhanced patient preparation for dialysis, improved patient psychosocial welfare and, importantly, an increased number of patients planned for and commencing home dialysis. This has empowered patients by giving them the confidence, knowledge and skills to be actively engaged in their own care. The project resulted in significant expenditure avoidance. Conclusion: Change management strategies with successful implementation are vital components of evolving clinical practice to achieve both clinical and organizational goals

Phonon emission and absorption in the fractional quantum Hall effect

We investigate the time dependent thermal relaxation of a two-dimensional electron system in the fractional quantum Hall regime where ballistic phonons are used to heat up the system to a non-equilibrium temperature. The thermal relaxation of a 2DES at $\nu=1/2$ can be described in terms of a broad band emission of phonons, with a temperature dependence proportional to $T^4$. In contrast, the relaxation at fractional filling $\nu=2/3$ is characterized by phonon emission around a single energy, the magneto-roton gap. This leads to a strongly reduced energy relaxation rate compared to $\nu=1/2$ with only a weak temperature dependence for temperatures 150 mK $< T <$ 400 mK.Comment: 4 pages, 3 figures; 14th International Conference on High Magnetic Fields in Semiconductor Physics, September 24-29, 2000, Matsue, Japa